| MEXICO CITY
MEXICO CITY Lizards are in danger of dying out on a large scale as rising global temperatures force them to spend more time staying cool in the shade and less time tending to basic needs like eating and mating.
Scientists warn in a research paper published on Thursday that if the planet continues to heat up at current rates, 20 percent of all lizard species could go extinct by 2080.
"The numbers are actually pretty scary," said lead researcher Barry Sinervo from the University of California Santa Cruz. "We've got to try to limit climate change impacts right now or we are sending a whole bunch of species into oblivion."
A mass extinction of lizards, which eat insects and are eaten by birds, could have devastating effects up and down the food chain, but the extent is difficult to predict.
Sinervo made models of lizards with thermal monitors and left them in the searing sun of southern Mexico to measure how the reptiles would react to temperatures at different altitudes.
Lizards bask in the sun not to relax but for self-preservation. As "ectotherms" they depend on the external environment to control their body temperature.
Unlike mammals, when the reptiles overheat they cannot sweat or pant and they have to retreat to the shade or burrow under a rock to cool down.
This biological quirk has already led to the extinction of 5 percent of lizard populations around the world, Sinervo said, as the creatures spend more time scrambling to find shade and less time doing what they need to do to survive.
"(Temperatures are rising) too fast. Evolution can't keep up," said Jack Sites, a herpetologist at Brigham Young University who collaborated with Sinervo's research.
Lizards come out during the day to warm up and use the time to find food needed to breed.
"The warming temperatures sort of eclipse that activity period ... It gets too hot to forage and they have to go back," said Sites.
"So they don't die directly but they can't reproduce. It only takes a couple of generations of that and the population is going to spiral downward until it goes extinct."
Elizabeth Bastiaans, a doctoral student in Sinervo's lab, started studying lizards in a wilderness outside Mexico City near the Aztec pyramids of Teotihuacan where tourists huff and puff up hundreds of stairs in the blazing sun.
"I've been out there doing a lot of sampling over the past few years and you see the lizards in the morning and you see them in the evening. But in the hottest part of day, it's just too hot, you don't see them at all," Bastiaans said.
Some of the spiny lizards with blue bellies she studies went extinct at lower, warmer altitudes. Some moved to higher, cooler ground but, as temperatures continue to rise, that habitat is shrinking.
"If the climate continues to warm, they are going to get pushed off the top of the mountains," Bastiaans said. "There is only so much mountain they can climb."
(Editing by Maggie Fox and John O'Callaghan)